A typical prior art head and disk system 10 is illustrated in block form in FIG. 1. In operation the magnetic transducer 20 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer 20, usually called a “head” or “slider,” is composed of elements that perform the task of writing magnetic transitions (the write head 23) in the magnetic medium included in the thin films 21 and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. The magnetic transducer 20 is positioned over points at varying radial distances from the center of the disk 16 to read and write circular tracks (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded. The magnetic domains in the media can be written longitudinally or perpendicularly. The read and write head portions of the slider are built-up in layers using thin film processing techniques. Typically the read head is formed first, but the write head can also be fabricated first. The conventional write head is inductive.
In a disk drive using perpendicular recording the recording head is designed to direct magnetic flux through the recording layer in a direction which is generally perpendicular to the plane of the disk. Typically the disk for perpendicular recording has a hard magnetic recording layer and a magnetically soft underlayer. During recording operations using a single-pole type head, magnetic flux is directed from the main pole of the recording head perpendicularly through the hard magnetic recording layer, then into the plane of the soft underlayer and back to the return pole in the recording head. The shape and size of the main pole and any shields are the primary factors in determining the track width.
Lead overlay designs for read sensors provide an advantage in improved stability and amplitude. The primary problem is the wide effective sensor width. In this design, track width controlled by the separation of the electrically conductive leads on top of the sensor is smaller than the full width of the sensor material. The lead overlay design moves the sensor free layer edges away from the active sensor region edges. A prior art spin valve head 12A with overlaid leads is illustrated in FIG. 2 in a section view taken parallel to the air bearing surface. Since the wafer is cut to expose the air-bearing surface, the view shown can also be described as being perpendicular to the surface of the wafer. The leads 36a, 36b as shown in this particular embodiment include three sublayers: tantalum 37, chromium 38 and rhodium 39. The tantalum and chromium layers serve as seed layers for the rhodium. The leads are deposited in contact with the top surface of the spin valve sensor 35 and the hard bias structures 33a, 33b. The gap layer 31 underlies the two hard bias structures 33a, 33b and the sensor 35. The hard bias structures 33a, 33b are shown as a single element even though they include more than one layer, e.g., a chromium layer (not shown) followed by a CoPtCr layer (not shown). The spin valve 35 is also illustrated as a single entity for simplicity even though it includes several layers.
In published U.S. patent application 20040257713 by Pinarbasi, et al., Dec. 23, 2004, a lead overlay magnetoresistive sensor is described with leads having substantially vertical end walls to accentuate sense current near the ends of the leads. Insulating layers isolate the hard bias layers from the path of the sense current. After a first photoresist liftoff structure has been removed, a second layer of photoresist is formed and patterned. The second layer of photoresist does not have the usual undercut liftoff structure. Instead, the second layer of photoresist has substantially vertical walls. Lead material may be conveniently chosen from low resistance, substantially inert electrical conductors such as rhodium, gold, ruthenium, and the like.
In published U.S. patent application 20030011943 by Webb, et al., Jan. 16, 2003, various embodiments of spin valve sensors with overlaid leads are described. A first embodiment for a bottom spin valve deposits a cap layer over the sensor then “notches” to expose the outer edges of the sensor. The overlaid leads are deposited in contact with the exposed side of the sensors. A second embodiment “notches” down through the free layer and the cap and then refills with copper and NiFe before depositing the overlaid leads. A third embodiment “notches” down through the free layer and partially into the spacer and refills with NiFe before depositing the overlaid leads. A fourth embodiment “notches” down through the free layer and completely through the spacer and refills with NiFe before depositing the overlaid leads. A top spin valve embodiment notches through the cap, antiferromagnetic (AFM) layer and optionally into or through the pinned layer before forming the leads that contact the pinned layer.
Published U.S. patent application 20050007706 by Dovek, et al., Jan. 13, 2005 describes a design in which an additional antiferromagnetic layer is added under the overlaid leads in a bottom spin valve design. The extra antiferromagnetic layer extends over the hardbias pads onto the top of the spin valve and is coterminous with the lead material. The longitudinal bias provided by the hardbias pads extends, it is said, without attenuation right up to the edges of the leads, so that the physical and magnetic widths of the sensor are essentially identical.
Lin, et al. (U.S. Pat. No. 6,729,014) describe a method for forming a top spin-valve with synthetic antiferromagnetic pinned layer (SyAP) GMR read sensor having a conductive lead overlay configuration that contacts the sensor at a position within the SyAP pinned layer. This is said to simultaneously assure improved electrical contact and destroy the GMR properties of the sensor at the junction to improve the definition of the sensor track width.
Shukh, et al. (U.S. Pat. No. 6,704,176) describe a spin valve sensor that includes free and pinned ferromagnetic (FM) layers, a conducting layer, contact leads, free layer biasing elements, and an antiferromagnetic (AFM) layer. The pinned layer has opposing ends, which define a width of an active region of the spin valve sensor having a giant magnetoresistive effect in response to applied magnetic fields. The free layer is positioned below the pinned layer and has opposing ends that extend beyond the active region. The contact leads abut the pinned layer and overlay portions of the conducting layer. The free layer biasing elements abut the ends of the free layer and bias a magnetization of the free layer in a longitudinal direction.
Damage to the edges of the sensor is believed to cause some signal loss in the free layer. The damage occurs during the track-width definition process. One way to avoid this damage is to have the physical edge of the free layer extended beyond the track-width region and define the read-width by magnetic or electrical means. These designs have been described in the prior art as exchange tab and lead overlay designs, respectively. However, these designs are known to have significant side-reading, making them unsuitable for very narrow track applications.